My issue is, I don't know how to create a MySensors sensor device on Vera. I can't use the normal include procedure as the sensor is on the gateway. But I tried anyway. by starting inclusion and resetting the gateway but to no avail.

What I have done for Vera to discover "Sensors" defined in the GW is this:

Add this to your GW sketch just after the port definition.

// How many clients should be able to connect to this gateway (default 1)
#define MY_GATEWAY_MAX_CLIENTS 2

Then when you have everything back up and running with Vera again you can connect another controller simultaneously called MYSController from a Windows computer.
When you are also connected from MYSController start the inclusion mode from Vera and then press the "Discover" button in MYSController.

Hello
Use the include procedure on the MYSensors Plugin Icon under settings you will see start and stop if all is working properly just press the start button you will see a dialog that tells you to activate the sensor you wish to add. If all goes correctly you will see a node added as well as the sensor. Now that is how it use to work with earlier Libraries if you are using 2.2 library I will presume it will work the same way.